1. Field of the Invention
This invention relates generally to an improved compact gas fired water heater for installation in recreational vehicles. Specifically this invention relates to a gas fired water heater of compact size with an improved combustion chamber that offers manufacturing, dimensional, cost and performance advantages over water heaters of this type currently available for such installations.
2. Description of the Related Art
While combustion chambers of various designs and configurations have been invented and used for furnace and other space heating applications, the methods employed over the years for combustion chambers for water heaters for the recreational vehicle market has been limited to direct vent type designs to meet rigid space limitations, test pressure requirements mandated by various regulatory codes, and design methods that will offer the most economical products to the RV manufacturer and the consumer. Consequently water heaters for recreational vehicles continue to be made with direct vent type combustion chambers employing either bent tubes that permit the inlet and outlet ends of the tube to both be positioned on the front of the water heater, or a larger diameter straight horizontal tube, closed at the rear, wherein gases enter the lower front half and exit the upper front half of the horizontally positioned tube.
With the bent tube type combustion chambers utilized in many RV water heater tanks today, hot gases are injected by a burner into an entrance of a tube in the lower portion of the water heater and exit the other end of the same tube in the upper portion of the water heater. Both ends, the entrance and exit, are positioned in front of the water heater, consequently the fronts of such water heaters must be large enough to accommodate the "U" shaped bend in the tube between the entrance and the exit. Due to the large radius required to made the "U" shaped bend without distorting the tube, the dimensions of such water heaters must be either wider or higher than a water heater employing the single straight tube type construction.
While water heaters utilizing a single horizontal tube type heat exchanger may have smaller width or height dimensions in front of the water heaters than water heaters made with bent tube type combustion chambers, they have other disadvantages. In this method of design, the products of combustion pass through the lower portion of the horizontal tube below an internal median divider that extends approximately four fifths of the way from the front to the back of the tube. The gases make a turn in the rear of the tube as they make contact with the rear closure plate, whereby they then move upward and exit through the top portion to the tube above the entrance. This construction while permitting compactness, has severe limitations in performance due to the slowing down of the movement of the hot gases resulting from the abrupt turn in back of the tube as well as the large internal diameter of the tube, generally 41/2" in the water heaters being offered today. A smaller tube diameter used in the same manner, while speeding up the flow of gases by having less internal area, would at the same time be ineffective since the total amount of heating surface making contact with the water would also be reduced accordingly, and in general, even the water heaters with the 41/2" diameter tubes have heating surface limitations below that of water heaters using bent tubes with separate inlets and outlets. In addition the total travel distance of the hot gases permitted with the straight horizontal tube type construction is also considerably less than the distance of travel within a combustion chamber that utilizes a separate inlet and outlet, and this further restricts the efficiency of such water heaters.
In a more recent invention, a combustion chamber is employed for compact water heaters that does not utilize a tube of any kind. This combustion chamber, similar to those used in furnaces in earlier inventions, utilizes two shell shaped halves welded together to form an internal flow pattern within a tank. While meeting the pressure requirements mandated for water heaters, this type of construction has several disadvantages inhibiting its use. Due to the large perimeters of the two halves utilized in its construction, a considerable amount of increased welding is required to weld the two halves together. In a typical water tank for a water heater of this type, the total amount of welding required for the tank is increased by approximately 20 to 25 percent. In the case of a glass lined tank, the increase in the area of the welded surfaces inside the tank, requires that additional cathode protection in the form of a larger anode be provided, further increasing the cost of the water heater to the consumer. Further, to insert the front of this type of combustion chamber into the front head of the water heater tank prior to welding, a large hole consisting of two circular holes joined together in the center with an additional narrow hole is required. This type of fabrication makes it difficult to perform automatic welding since the surfaces where the front head and combustion chamber come in contact are on different radiuses. Fit up problems between the head and combustion chamber complicate the problem even further, since minor variances in the size of the dimensions of the welds in the areas on the combustion chamber that must protrude through the tank head can result in either the combustion chamber not fitting through the pierced holes in the head, or a loose fit in the head which in turn makes it impossible to weld the combustion chamber successfully into the head with automatic welding.
A need therefore exists for a water heater with a combustion chamber design that will enable the water heater to meet the smallest front dimensional requirements for small compact water heaters for recreational vehicles, permit the best possible economies by reducing the total amount of welding required, permit fully automatic welding of the combustion chamber into the tank head, insure long tank life in the case of glass lined tanks without adding additional anode surface, and at the same time enable the water heater to obtain a higher recovery and better efficiency than water heaters of this type currently available to the consumers.
The present invention fulfills this need and provides further related advantages.
Various methods and designs have been used for combustion chambers over the years, most of which were used for furnace and other types of space heating applications. None of the referenced patents or prior art reveals or suggests a combustion chamber which is fabricated by inserting and welding two lengths of tubing into a coupler to make a smaller radius turn than could otherwise have been made by a bend, and then in turn mounting the combustion chamber horizontally into the tank by inserting the two opposite ends of the tubing through the front head of the tank and welding them into position. These prior art references are:
______________________________________ U.S. PAT. NO. INVENTOR ______________________________________ 4,771,762 Bridegum 3,405,690 Burrus et al. 3,062,233 Hammersley 3,056,400 Hammersley et al. 2,796,860 Pinkus et al. ______________________________________